Stage 61 — PWA Authenticated API Data Layer

Adds pwa/api-data.js, a small authenticated read-only data layer that uses the Stage 60 memory-only auth session.
Exposes methods for /me, /profile, /dashboard, and /permissions.
No API responses, tokens, or credentials are persisted by this layer.
Service worker cache is v12 and only includes the public PWA helper files; API/private application routes remain excluded.
No database changes and no SQL import.
